no-undefined-server-variable

Requires every server URL placeholder to be defined and, by default, every defined variable to be used.

Attribute	Value
Category	Metadata
Maturity	Baseline
OpenAPI	OpenAPI 3.0, 3.1, 3.2
Starter	Warning
Lenient–Complete	Error

Intent

Server URL templates and their variable definitions must stay synchronized for reliable URL expansion.

Flags

• Each {name} found in a server URL with no exactly matching variable definition.
• Unless allowed, each defined variable not present in the URL.

All parsed server locations are inspected; matching is case-sensitive.

Does not flag

Synchronized variables. With allowUnusedVariables: true, unused definitions are accepted, but undefined URL placeholders are still reported.

See it fail

servers:
  - url: https://{environment}.example.test
    variables:
      region:
        default: us

This reports undefined environment and unused region.

Fix it

servers:
  - url: https://{environment}.example.test
    variables:
      environment:
        default: production

Configure

profiles:
  default:
    rules:
      extends: [recommended]
      override:
        no-undefined-server-variable:
          severity: error
          allowUnusedVariables: true

Nearby: no-server-variables-empty-enum.